Modern laser printers operate in essentially the following manner: An electrostatically charged drum is exposed to light on portions which correspond to the light and dark portions of a digital image to be printed on a page. The exposed portions of the drum are discharged, while the remaining drum portions remain charged. The charged portions of the drum attract particles of dry powdered ink called toner. Paper is then pressed about the drum such that the toner leaves an image imprint on the paper. The paper is then run through a heated roller which, through heat and pressure, fuses and bonds the toner to the paper, resulting in a piece of paper imprinted with the image desired to be printed. Modern copiers operate in a similar manner, wherein the electrostatically charged drum is exposed to light on portions that correspond to the light and dark portions of an image to be copied. These portions of the image are determined by exposing the image itself to a light source and determining which portions reflect the light and which absorb it.
The toner used by the printer or copier is typically stored in replaceable cartridges. When toner in the cartridge is used up, the empty cartridge is removed from the printer and replaced with a full cartridge.
Toner cartridges are manufactured in many different configurations and sizes. In many cases, a manufacturer will produce cartridges that are substantially similar in overall configuration to each other, but differ in size. This size difference may exist for a variety of reasons, 1) to contain varying amounts of toner to accommodate varying amounts of toner use (light duty vs. heavy duty usage), 2) to conform to various printer/copier configurations (smaller or light duty machines vs. larger or heavy duty machines), or to conform to differences in how individual printer/copier models are designed and manufactured.